This application claims the priority of German patent document 10 2008 047 793.1, filed Sep. 17, 2008, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a load introducing element for a control surface of an aircraft or a spacecraft, as well as to a method for manufacturing the same, and to an aircraft including the same.
Larger control surfaces of commercial passenger airplanes often include ribs, which are mounted on at least one spar and are enveloped by an outer skin. Control surfaces with a relatively complex movement pattern (which, for example, goes well beyond a simple flapping) require a special mounting and special drive elements. Thus, for example, in order to increase the lift coefficient in certain flight phases Fowler flaps move in both a translatory and rotational manner and, correspondingly, are mounted in a moveable manner (for example, on pendulum supports, roller carriages or the like) and deflected by a pivotably mounted actuator.
Therefore, a control surface design which is adapted to the above features includes at least one rib that serves as the interface between loads that occur on the control surface and the structure of the craft. Furthermore, this rib can be used to mount the control surface. Currently such “load introducing ribs” are manufactured as a metal part to be milled—even in the case of a total CRP [carbon fiber reinforced plastic] construction of the control surface itself—and are mechanically connected to the control surface (for example, by interlocking connecting elements).
The production of such a metal load introducing rib is very expensive because it involves mechanical machining of a solid workpiece and, thus, results in high costs. Furthermore, there is the drawback that in the case of control surfaces that are made of fiber reinforced composite materials, a metal load introducing rib has a different heat expansion behavior than the control surface, attached to it. The result may be mechanical stresses that can be compensated only by means of suitably designed structures or by flexible mountings. Consequently such metal load introducing ribs are extremely disadvantageous in modern commercial passenger airplanes with control surfaces that are made of fiber reinforced composite materials.
One object of the present invention is to provide a load introducing element that does not suffer from the above described drawbacks; but rather is as simple as possible to produce, weighs as little as possible, and has a heat expansion behavior that is similar to that, for example, of a control surface that is made of a fiber reinforced composite material.
This object of the invention is achieved by the load introducing element according to the invention, as well as a method for manufacturing such a load introducing element, and an aircraft with at least one control surface and at least one such load introducing element.
According to one aspect of the invention, the inventive load introducing element has a first component and a second component which fulfill two different functions. When viewed from the shape of its upper surface, the first component acts as a conventional rib, making it possible to achieve a covering by way of the inventive load introducing element with a continuous contour. The second component has at least one eye for receiving bearing means for mounting the control surface, so that the mechanical load introduction is achieved in essence by means of the second component, which transfers the load into the first component that is connected to said second component.
An additional very important aspect of the invention lies in the fact that the individual components of the inventive load introducing element (for example, the first component and the second component) are not produced separately from each other and are not subsequently adapted to each other and connected together in an expensive manner. Rather the individual components, composed of one layer or multiple layers of fibrous preforms, are laid and then are jointly infiltrated and cured, for example, in an appropriate mold. In this way it is possible to produce the individual components in the form of fibrous substructures comprising multiple layers of a fibrous perform, and then to assemble these fibrous substructures in the mold, in order to infiltrate and cure jointly the whole assembly of fibrous substructures.
According to this method, the load introducing element of the invention exhibits very uniform material properties, and due to the joint infiltration and curing, the individual components are also connected together in an optional way to form an integral module made of fiber reinforced composite material. Similarly the individual components can be optimized with respect to the ensuing force directions, for example, by means of suitably oriented fibers. Such an optimization could not be achieved if the components were made of metal, because such an ultra lightweight member, which is optimized for force directions, cannot be produced by machining or deformation. With mechanical processing tools the cost would clearly be too high, and the resulting component would be too cost intensive.
Furthermore, the weight can be significantly reduced by manufacturing from a fiber reinforced composite material, comprising individual fibrous preforms and a matrix material, so that a control surface that is equipped with a load introducing element according to the invention, can be significantly lighter than a conventional control surface with a metal load introducing rib.
Another important aspect of the invention is that the heat expansion behavior of a whole control surface with a load introducing element of the invention is homogeneous, so that no structural or mechanical adjustments are required to accommodate different heat expansion behaviors between the control surface and the metal load introducing rib.
In a preferred embodiment of the load introducing element of the invention, the first component has a surface area that is adapted to the inner contour of the contour surface, so that a covering can be carried out, as in the case of all reinforcement ribs of the control surface. A cross sectional profile of this first component of the preferred embodiment has two or more essentially straight legs which are connected together on their upper side by means of an upper edge that is adapted to an upper contour of the control surface. Furthermore, at least one first flange for connecting to at least one structure of the control surface is arranged on the end of the first component that faces away from the upper edge. In this way the first component can exhibit a cross sectional profile that is shaped in essence like an omega, and has sufficient design space for housing a second component. Furthermore, this profile exhibits an especially advantageous moment of surface inertia for absorbing mechanical flexural or torsional loads.
In a preferred embodiment of the load introducing element of the invention, the first flange and the first component are constructed from common layers of material in the form of fibrous structures, fiber braids, composite fiber mats or other similarly constructed layers of a fibrous material. As a result, it is possible to minimize the risk of mechanical damage (resulting, for example, from fastening the flange to the first component) between the first flange and the first component.
Furthermore, the production of such a component is simplified and is, consequently, more cost effective. Finally even the introduction of force can be designed so as to be very uniform and continuous between the flange and the first component, so that it is possible to make the wall thickness correspondingly thin.
In an especially preferred load introducing element of the invention, the second component is enveloped (at least in certain areas) by the first component. In this way it is also possible to achieve an especially uniform and continuous transmission of force between at least one eye of the second component into the first component of the load introducing element of the invention. In addition, the free space that is available in the first component is occupied by the second component and, thus, additionally reinforces the first component.
It is especially preferred that the second component exhibits a greater wall thickness in an area that includes the at least the one eye, than in an area that is enveloped by the first component. In the area that includes the at least the one eye, bushings, bolts or the like are usually used by way of a borehole and/or opening, for the purpose of transferring forces and movements of bearing means to the second component, so that the mechanical stress of this area is especially significant. In order to prevent the structure of the second component from suffering any damage, the wall thickness in this area must be dimensioned correspondingly. The resulting stresses are distributed outside this area into the second component, which needs a thinner wall thickness to cope with the loads.
It is especially preferred that the second component exhibits a profile cross section that is essentially U shaped. Such a construction allows the second component to be housed very easily in a first component, which has the shape, for example, of an omega, and, moreover, exhibits adequate design space to house other components. This structure makes possible an especially optimal moment of surface inertia because the leg of the U profile is positioned at a distance.
Similarly it is preferred that the load introducing element of the invention exhibits at least one material layer, the cross section of which is L shaped. Furthermore, said material layer is applied simultaneously, at least in certain areas, on at least one element of the group, composed of the first component, the second component and the first flange. For example, this could be a part of the eye and is applied from the outside on the second component. In this case the angle is below the flange of the first component. On the other hand, the first flange could be further reinforced in relation to the first component, a state that could be achieved by laying an L shaped layer of material on the first flange when affixing to a wall surface of the first component.
Furthermore, it is especially preferred that the load introducing element of the invention has at least one wall plate that is integrated into the at least one second component. Such wall plates could be used to distribute loads in the spanwise direction over both halves of the second component and eventually to connect again in a load bearing manner the load bearing structures of the control surface, which are separated by the load introducing element of the invention. This could be, for example, a front spar or the like. Working on this basis, there are preferred positions for such wall plates, for example, in the area of the eyes.
In addition, it is also preferred that the load introducing element of the invention has at least one second flange that is aligned substantially transversely to the direction of stretch of the load introducing element. Such a second flange makes it possible to attach the load introducing element of the invention to additional load bearing structures of the control surface—for example, a rear spar and/or an auxiliary spar—that is positioned in the spanwise direction.
In addition, it is preferred that the first component includes a provision for connecting to a drive armature. The drive armature allows the load introducing element of the invention to be deflected in a separate component, so that the receiving points for the actuators can be designed in an optimal way, without having to compromise the integrity of the load introducing element and the points for receiving the bearing means. Since the load introducing element of the invention does not have unlimited design space inside the control surface, this approach offers itself, because the drive armature could be positioned, for example, laterally to the load introducing element of the invention.
Finally it is advantageous if the load introducing element of the invention is an integral component.
The invention also includes a method for producing such a load introducing element, comprising cutting to size preformed fibrous substructures out of a fibrous material, draping these fibrous substructures in order to mold the first component, the second component and the first flange in the form of a single semi-finished product, inserting the semi-finished product into a mold, initiating the matrix material and then curing. This procedure achieves an integral component in the form of the inventive load introducing element that is limited to a few process steps and, hence, can be carried out at a low cost. In order to ensure the dimensional stability of the load introducing element of the invention, conventional mechanical machining devices can also be used additionally for subsequent finishing work, the cost of which, however, is unrelated to the cost of machining a solid part to be milled.
Finally the invention also includes an aircraft or spacecraft which has at least one control surface with at least one load introducing element according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.